A currently utilized technique for dyeing keratinic fibers, and especially living human hair, comprises applying to the hair, in the presence of an oxidizing agent added at the moment of use (generally hydrogen peroxide), a dye composition comprising a mixture in an appropriate cosmetic support, of compounds belonging to one or the other of the two following classes.
The first class of compounds, generally called "oxidation bases" is principally constituted by paraphenylenediamines or paraaminophenols which, on oxidation, produce para benzoquinonediimines or parabenzoquinonemonoimines.
The second class of compounds, generally called "couplers" include, especially, metaaminophenols, metaacetylaminophenols, metadiamines and metadiphenols. These compounds which when reacted with benzoquinone mono- or di-imines produce dyes which, depending upon their structure, are called indophenols, indoanilines or indamines.
These dyes, which provide a range of shades of exceptional richness, importantly are characterized by the luminosity and the richness in glints of dyeings or colorations they impart to the fibers dyed therewith.
However, when a complex dye composition is employed, i.e. a composition which includes several bases and several couplers, it is very difficult to foresee in the final shade the contribution of each possible couple of oxidation base and coupler. In other words, on the one hand, it is very difficult at the outset to predict with any exactitude the final shade that will be attained and, on the other hand, for a given dye composition it is not often easy to be assured of a perfectly reproducible result. These difficulties are increased by the fact that different secondary reactions can modify the final shade, such secondary reactions including, for instance, formation of Bandrowsky base type compounds starting with oxidation bases; recondensation of a molecule of an oxidation base on certain indophenols or on certain indoanilines or indamines; and formation of quinones and the like.
Heretofore it has also been proposed to use in the dyeing of hair some indoanilines which are well defined compounds and which impart to the hair essentially perfectly reproducible shades.
However, some inconvenience has been experienced in the use of these compounds since they possess only a slight affinity for keratinic fibers under conventional conditions for dyeing hair.